Conventional practice in raising cattle in most countries, is to confine them in feedlots or feedyards, where they are fed high-value feed mixes that are enriched with proteins, carbohydrates, fats, vitamins and minerals for the purpose of achieving a rapid gain in weight. Hundreds of such feedlots or feedyards exist in the United States alone, each one of which may contain as few as 2,000 or as many as 100,000 head of cattle, all confined in a relatively small area.
Studies establish that cattle are relatively poor in converting their food, and particularly high-value feed mixes, to useful meat and tissue, and, in fact, it has been shown that an average of 18 pounds (dry weight) of high-value feed mixes per day must be fed to a typical 700 pound animal for its maintenance and to achieve a daily weight increase in the range of 21/2 to 23/4 pounds during its confinement in a feedyard. Where an average animal voids approximately 8-8.5 pounds by dry weight of manure and urine during a 24 hour period, it is clear that 30% to 40% by weight of the food value passes directly through and is present in its waste products.
In copending patent application Ser. No. 339,892, PROCESS FOR RECOVERING NUTRIENTS FROM ANIMAL WASTES by Franklin C. Senior, filed Mar. 9, 1973, there is described a method for recovering food values from manure, but which process does not remove certain so-called ash and other inorganic compounds normally present in the manure and which have no nutritional value. That is, since a considerable number of the feedlots at the present time have earthen floors, manure deposited thereon will automatically pick up a significant amount of inorganic salts, earthy oxides, and the like, as well as trace amounts of heavy metal oxides, sulfides, and minor amounts of compounds of lead, mercury, molybdenum, antimony and chromium. Since the recovered nutrients are contemplated primarily for recycled animal feed, it is clear that unless these various water soluble and water insoluble inorganic compounds (which will be referred to hereinafter generally as ash) are removed, they can build up to a level which might be dangerous to the health of the animals.
The ash components in new, i.e., unrecycled, feed are derived primarily from the plants and grains comprising the food mix and this can vary considerably from yard to yard with composition change being a function of the soil in which the food stock plants and grains are grown. Examinations of various feedlot mixes establish that on a dry basis, they are composed of 6%-7% ash. As a specific example, in a feedlot which averages approximately 18 pounds per day of dry weight feed for an animal of 650-700 pounds gross weight, there would be produced on an average about 8 pounds per day of dry weight manure as well as urine including a variety of different salts. The ash content in the daily ration of a feed mix consisting essentially of chlorides, sulfates and oxides of light and heavy metals, would be approximately 6.7% or 1.2 pounds. It has also been found that a large percentage of the ash compounds in the animal waste matter are soluble chlorides, sulfates and the like of sodium and potassium, for example, which may either remain in the animal or be voided in its urine or its manure. Therefore, from a practical standpoint, the dry or solid manure would carry about 8-10% ash or equivalent to approximately 0.60 pounds of the 8 pounds of dry manure, averaging out to approximately 10% of the dry manure. Substantial amounts of the original solids such as soluble salts in the urine leached or otherwise percolate into the earthen floor of the feedyard.
In the previous general example, the ash has been derived solely from the feed mix fed to the animal. However, when the manure has been deposited upon an earthen floor, analysis establishes that the dry manure always contains 27-32% ash. Therefore, for an average animal contained in an earthen floor feedlot, approximately 2.4 pounds per day of ash is present in its manure. This additional 2.4 pounds per day of insoluble ash that comes from the earthen floor is produced primarily by the animal pawing the manure and earth together, the wind blowing the dirt or the animal eating a certain amount of the soil mixed with his feed.